Re: Sockets in a DLL, access violation

I have a DLL that opens a simple UDP socket and does basic operations. My DLL
is called from a 3rd party app that I neither have control over nor source code
for. Some calls work OK, but with others I can a unhandled exception, access
violation. I've seen the exception on ReceiveFrom, SendTo, Close, etc. and in
all cases it looks like the function calls had all good parameters.

After doing a bunch of Googling and reading, it looks like the most common cause
of this is creating the socket in one thread and accessing it from another.
(The other common problem, a bug in MSVC 6 with MFC DLL as a static linked
library, shouldn't be an issue since I have the latest service pack (SP 6)
installed.) So I am suspecting a thread problem. However, as I mentioned
above, I am in a DLL and don't have control over the calling app, so I can't
confirm the thread issue and if I could, I'm not sure how to solve it. So my
questions are: 1) is there a way to tell if my DLL code is being called from
different threads? and 2) if so, how can I write my sockets code in such a way
as to survive being called from different threads?

My set-up is MSVC 6.0 SP6, Windows 2000, MFC 4.2 as a shared DLL. Any help is
appreciated!